Variable valve actuation mechanisms for altering the valve timing of internal combustion engines are well known. One such known approach relies on a control shaft arm clamp to position and lock the control shaft arm in place in order to set valve lift timing. Present clamp designs cannot meet more stringent engine manufacturing requirements for fine adjustment of the relative rotary position of the control arm on the control shaft so that air flow to each cylinder is the same. Further, there must be assurance that, after being positioned correctly, the control arm cannot slip around the control shaft, which could cause imprecise valve lift timing and possible engine damage.
The control arm position is used to calibrate the VVA mechanism so that the airflow to each engine cylinder is the same. A prior art adjustment method requires the clamp to be loosened so that it can be angularly repositioned about the control shaft. After repositioning, the clamp screw is retightened. A problem with this method is that, once loosened, the clamp moves freely, both axially and tangentially around the control shaft. An operator making the adjustment can have great difficulty in making a very small angular adjustment while maintaining accurate axial position. Even if the axial position were not a problem, it is quite difficult for an operator to precisely and repeatably make a very small angular adjustment, for example, 0.1 degree, to the control arm clamp.
What is needed is an improved clamp whereby very small and predictable angular adjustments may be made while maintaining invariant axial position.
What is further needed is redundant means in an improved clamp so that, if the clamp should come loose or is not properly tightened, the axial and angular position of the clamp with respect to the control shaft cannot change significantly.
It is a principal object of the present invention to permit fine adjustment of angular position of a clamp on a shaft.
It is a further object of the invention to provide such adjustment without causing or allowing axial movement of the clamp on the shaft.
It is a still further object of the invention to provide such adjustment which is then redundantly locked into the mechanism.